The effect of sintering temperature, and $Al_2O_3$ and SrO on sintered density and piezoelectric properties in $Pb(Mg_{1/3}Nb_{2/3})_0.125 Ti_{0.435} Zr_{0.44} O_3$ near the morphotropic phase boundary has been studied.
The specimens of disc shape were sintered at 1220℃, 1240℃, 1260℃, 1280℃, and 1300℃ for $1\frac{1}{4}$ hours in $O_2$ atmosphere. Partial substitution of Sr atom for Pb decreased the sintered density. Also when $Al_2O_3$ was added in $Pb_{0.95}Sr_{0.05}$ $(Mg_{1/3} Nb_{2/3})_{0.125}$ $Ti_{0.435} Zr_{0.44} O_3$, the maximum density was obtained when 0.25wt.% $Al_2O_3$ was added. However, when more than 1.0wt% $Al_2O_3$ was added, the sintered density was decreased. Optimum sintering temperature existed in the 1260℃ ∼ 1280℃ range.
As $Al_2O_3$ was added in $Pb_{0.95} Sr_{0.05} (Mg_{1/3} Nb_{2/3})_{0.125} Ti_{0.435} Zr_{0.44} O_3$, mechanical Q-factor $Q_M$ increased, planar coupling factor $K_p$ stayed relatively constant and dielectric constant was decreased. Excessive addition of $Al_2O_3$ above 1wt.%, however, decreased planar coupling factor kp.
Electron microprobe analyses confirmed that above the added concentration of 0.5wt.% $Al_2O_3$ tended agglomerate at the grain boundary in spherical shape, while portion of $Al_2O_3$ was also present in the grain.
The amount of space charge appears to increase with increasing amount of $Al_2O_3$. In the mean time, the mobility of domain decreased, and therefore the mechanical Q-factor increased.
When 5mole % Sr atom was substituted for Pb, planar coupling factor $K_p$ and dielectric constant increased, while on the other hand mechanical Q-factor $Q_M$ decreased. When 10 mole % Sr was substituted, however, the contrary effect was observed. Curie temperature decreased in the ratio of 9.2∼9.5℃/mole Sr by the substitution of Sr for Pb.
